Field of the Invention
The present invention relates to an inertial drive actuator that causes a movable member to move in a predetermined direction.
Description of the Related Art
There is a known actuator in which saw-tooth pulses are supplied to an electromechanical transducer coupled with a drive shaft to shift the drive shaft in the axial direction, thereby moving a movable member frictionally coupled with the drive shaft in the axial direction. (Such an actuator will be hereinafter referred to as an “impact drive actuator” or “inertial drive actuator”.)
Such an impact drive actuator is disclosed in Japanese Patent Application Laid-Open No. 2007-288828. FIG. 11A shows the construction of the impact drive actuator. A vibration member 103 is inserted through holes provided in standing portions of a support member 101 and movable in the axial direction of the vibration member 103. One end of the vibration member 103 is fixed to one end of a piezoelectric element 102, the other end of which is fixed to the support member 101.
Consequently, the vibration member 103 vibrates in the axial direction with the vibration of the piezoelectric element 102. A movable member 104 also has two holes, through which the vibration member 103 is inserted. A leaf spring 105 is attached to the movable member 104 from below. A projection provided on the leaf spring 105 is pressed against the vibration member 103. The pressure exerted by the leaf spring 105 brings the movable member 104 and the vibration member 103 into frictional coupling with each other.
FIGS. 11B and 11C show waveforms of driving pulses for driving the impact drive actuator. FIG. 11B shows a waveform of driving pulses for moving the movable member 104 to the right, and FIG. 11C shows a waveform of driving pulses for moving the movable member 104 to the left. The operation principle of the impact drive actuator will be described in the following with reference to these driving pulse waveforms. In the following description, it is assumed that the direction in which the piezoelectric element 102 expands is the left, and the direction in which the piezoelectric element contracts is the right.
When the movable member 104 is to be moved to the right, the driving pulse waveform shown in FIG. 11B is used. The driving pulse waveform has steep rise portions and gradual fall portions. The steep rise portions of the driving pulse waveform cause the piezoelectric element 102 to expand quickly. Because the vibration member 103 is fixed to the piezoelectric element 102, the vibration member 103 moves to the left at high speed with the quick expansion of the piezoelectric element 102. During that time, the inertia of the movable member 104 overcomes the frictional coupling force between it and the vibration member 103 (i.e. frictional force between the vibration member 103 and the movable member 104 pressed against it by the leaf spring 105), and therefore the movable member 104 does not move to the left but stays at its position.
The gradual fall portions of the driving pulse waveform causes the piezoelectric element 102 to contract slowly. Then, the vibration member 103 slowly moves to the right with the slow contraction of the piezoelectric element 102. During that time, the inertia of the movable member 104 cannot overcome the frictional coupling force between it and the vibration member 103, and therefore the movable member 104 moves to the right with the movement of the vibration member 103.
On the other hand, when the movable member 104 is to be moved to the left, the driving pulse waveform shown in FIG. 11C is used. The driving pulse waveform has gradual rise portions and steep fall portions. The gradual rise portions of the driving pulse waveform cause the piezoelectric element 102 to expand slowly. Then, the vibration member 103 moves slowly to the left with the slow expansion of the piezoelectric element 102. During this time, the inertia of the movable member 104 cannot overcome the frictional coupling force between it and the vibration member 103, and therefore the movable member 104 moves to the left with the movement of the vibration member 103.
On the other hand, during the steep rise portions of the driving pulse waveform, the inertia of the movable member 104 overcomes the frictional coupling force between it and the vibration member 103, as with the case described above with reference to FIG. 11B, and therefore the movable member 104 does not move to the right but stays at its position.
Since the vibration member 103 is always pressed by the leaf spring 105, the movable member 104 is frictionally supported by the vibration member 103. In consequence, when the movable member 104 is stationary, its position is maintained.
As described above, the impact drive actuator utilizes the frictional coupling of the movable member 104 and the vibration member 103 provided by the leaf spring 105 and the inertia, and it can move the movable member 104 using driving pulse waveforms shown in FIGS. 11B and 11C.